At the same time, Wilma was pounding the western tip of Cuba, where the government evacuated more than 500,000 people.

Forecasters said Wilma could bring as much as 40 inches of rain in parts of Cuba.

Evacuees in Mexico spoke of miserable conditions in the shelters, no food and leaking roofs.

Rachel and Carl Farricker, from Altham, Lancashire, are part of a group of more than 1,000 tourists, including around 80 Britons, forced to sleep in a sports hall in Cancun.

Mrs Farricker said she had heard huge crashes and bangs and that water was pouring in.

She said: "The power has already gone out eight or ten times and the lights go out."

The Foreign Office has urged Britons in the area to monitor local news and weather reports.

Embassy staff were deployed to the region and a consular rapid deployment team from London was on stand-by.

Wilma approached Mexico with the same strength as Hurricane Katrina, which slammed into Louisiana on August 29, killing more than 1,200 people.

Max Mayfield, director of the US National Hurricane Centre, said by tonight Wilma should be a much weaker storm.

But he urged those monitoring its progress in Florida not to get complacent, warning that it would remain "very powerful".

If it follows its predicted path 400-mile wide Wilma will be the seventh hurricane to hit Florida in 14 months. Traffic jams had already began forming across the south west coast as people put up shutters and stocked up on food and bottled water.

Some 20,000 Britons are currently in the state, according to the Association of British Travel Agents. The majority are in Orlando on the north east coast.

* Those concerned about Britons in Mexico can call the Foreign Office on 020 7008 1500.